The present invention relates to an antibacklash rack assembly and, more particularly to such assembly in combination with a rotatable gear in which backlash is substantially reduced during operation.
Various assemblies have been employed in the past for the purpose of reducing backlash in the operation of meshed gears, including meshed pinion gears and pinion gears which mesh with longitudinally moving toothed racks. Such prior antibacklash assemblies have generally included mechanisms which act on the pinion gear to reduce the backlash, rather than on the rack where the assembly is a rack and pinion assembly.
In a few prior rack and pinion gear assemblies, mechanisms have been provided which act upon the rack to reduce backlash. However, these mechanisms are generally relatively complex or they require the manufacture and positioning or relatively complex or intricate rack parts to achieve the antibacklash function. Moreover, in these prior assemblies, the antibacklash mechanisms do not generally move or exert their antibacklash force in the same longitudinal direction in which the rack moves and in which the backlash impact forces would tend to act.
An antibacklash rack assembly incorporating the principles of the present invention is both simple in construction as well as manufacture, and effectively functions to reduce if not eliminate altogether backlash which might occur in a rack and pinion assembly. In an antibacklash rack assembly incorporating the principles of the present invention, the antibacklash force and action is imparted to the rack in the same longitudinal direction in which the rack normally moves and in which the backlash impact forces would be directed if backlash was to occur. Moreover, the antibacklash assembly of the present invention readily compensates for any wear on the rack or pinion teeth to eliminate backlash over the life of the assembly.
In one principal aspect of the present invention, an antibacklash rack includes a first longitudinally extending rack member having gear teeth which extend transversely thereof and which are adapted to receive and engage at least one tooth of a gear to mesh therewith. This first rack member is movable in a longitudinal direction. A second longitudinally extending rack member also has gear teeth extending transversely thereof and in substantially the same direction as the teeth of the fist rack member. The teeth of the second rack member also are adapted to receive and simultaneously engage the same tooth of the gear of that which meshes with the teeth of the fist rack member and the second rack member is also longitudinally movable with the first rack member. Urging means exerts a force on the second rack member in the longitudinal direction to urge at least one of the teeth on the second rack member in the longitudinal direction and in offset relationship to the teeth of the first rack member which engage the tooth of the gear which meshes with the teeth of the fist rack member. Thereby, the tooth of the gear is forced into engagement with a tooth of the first rack member and held in engagement therewith such that the opposite sides of the tooth on the gear which meshes with the teeth of the rack members are simultaneously positioned and held in engagement with at least one tooth on each of the first and second rack members to prevent backlash upon movement of any of the teeth.
In another principal aspect of the present invention, an antibacklash rack and rotatable gear combination includes at least one rotatable gear having gear teeth thereon and means for transmitting a mechanical torque relative to the rotatable gear. A first longitudinally extending rack member has gear teeth extending transversely thereof which mesh with at least one tooth of the rottable gear and the first rack member is moveable in a longitudinal direction. A second longitudinally extending rack member also has gear teeth extending transversely thereof and an substantially the same direction of the teeth of the first rack member. The teeth of the second rack member also simultaneously mesh with at least the one tooth of the first rack member, and the second rack member is also longitudinally movable with the first rack member. Urging means exerts a force on the second rack member in the longitudinal direction to urge at least one of the teeth on the second rack member in the longitudinal direction and in offset relationship to the teeth on the first rack member to engage at least one tooth of the rotatable gear and force that tooth into engagement with the tooth of the first rack member and hold it in engagement therewith. Thereby, opposite sides of the one tooth of the rotatable gear are simultaneously positioned between and held in engagement with at least one tooth on each of the first and second rack members to prevent backlash on movement of the teeth. Means is also provided for transmitting a linear force relative to the rack members.
In still another principal aspect of the present invention, the foregoing urging means comprises a spring which urges the second rack member to move in at least one longitudinal direction and relative to the first rack member.
In still another principal aspect of the present invention, a elongate guide means is provided which extends between the rack members, the guide means being fixed to one of the rack members and the outer rack member being slidable relative to the guide means.
In still another principal aspect of the present invention, the foregoing guide means comprises at least one elongate pin.
In still another principal aspect of the present invention, the foregoing guide means is fixed to the first rack member and the second rack member is slidable relative to the guide means.
In still another principal aspect of the present invention, the foregoing spring is mounted on the foregoing pin.
In still another principal aspect of the present invention, the first rack member includes an elongate opening therein and the second rack member is positioned in the opening for longitudinal movement in the opening relative to the first rack member, and the teeth of the respective rack members are longitudinally offset relative to each other by the urging means.
In still another principal aspect of the present invention, the urging means comprises a spring in the opening which bears against the rack members.
In still another principal aspect of the present invention, the force exerted by the urging means is greater than the torque on the means for transmitting a mechanical torque relative to the rotatable gear.
In still another principal aspect of the present invention, the means for transmitting a mechanical torque relative to the rotatable gear is a rotatable shaft on the gear, and the means for transmitting the linear force relative to the rack members is a fluid piston.
In still another principal aspect of the present invention, the foregoing piston is driven by fluid and the rotatable gear and shaft are driven by at least one of the rack members.
These and other objects, features and advantages of the present invention will be more clearly understood through a consideration of the following detailed description.